Normal human aging is known to influence a variety of neurobiological and psychological variables. Many such variables have been studied in a select population of elderly volunteers (aged 75 to 95) (the Longitudinal I Study at the Duke Center for the Study of Aging and Human Development) for whom data are already available (spanning the past 18 years). The purpose of the present study is to expand the data on this subject population to include sleep pattern measurements. Sleep variables and particularly rapid eye movement REM sleep time, are known to correlate significantly with intellectual functioning among normal elderly and brain damaged subjects. It is hypothesized that selected group variables will also correlate well with the other physiological and psychological measures known to be sensitive to aging influences. Longitudinal Data is already available for the cerebral blood flow decline, the slowing of EEG alpha frequencies, Wechsler Adult Intelligence Scale performance scores, paired associate learning and Weschsler memory delayed recall task, reaction time evaluations, etc. These measures will be examined for their interrelationships with sleep variables. In addition, the sleep variables themselves will be evaluated as to their relative sensitivity to the influences of aging.